With the popularization of mobile communications, cell phones have become a communication device that are carried around daily by people, and instant messaging has quickly become one of the commonly used ways of communication, too. The instant messaging has a fast transmission speed, and it can transmit messages immediately to the cell phone of a receiver and can learn whether the receiver has read the messages or not from the message transmission status, so instant messaging has replaced most of the functions of e-mails and facsimiles and become one of the indispensable communication means at present. Since instant messaging can transmit messages to the receiver instantly and accurately, it has been used by some people to forcibly send some commercial advertisements, personal advertisements or even adult messages or some unpleasant messages to users without the users' consent. When users receive such instant messages, they found that the messages are usually useless messages sent from strangers, namely, the so-called junk messages, so they will usually delete these junk messages. But as the number of junk messages is increasing, deleting such messages takes more time, and network frequency bandwidth and server storage space are wasted as well, and even the users have to pay extra data communication fees, so this has seriously affected normal communication of people. In this case, it is an urgent problem to be solved as to how to prevent such junk messages from being sent to users through instant messaging.